(1) Field of the Invention
The present invention relates to an apparatus for detecting the edge of a semitransparent plane substance, specifically, for example, an automatic teller machine which discriminates between different types of paper currency.
(2) Description of the Prior Art
An apparatus for detecting the edge of a semitransparent plane substance is used, for example, for detecting the width, and thus, discriminating the type of, paper currency.
Since paper is semitransparent, however, it cannot completely interrupt light from a light source. Also, the thickness, design, color, and quality of the paper affect the amount of light passing therethrough. This makes precise detection of the width of paper currency of various paper qualities, designs, or colors difficult. In practice, it limits the type of currency which may be precisely detected. Also, the amount of light from the light source varies, causing variation of the light detected through the paper.
The detecting accuracy of the apparatus is further limited according to where the paper passes through the apparatus, as, usually, only a single photosensor is used to receive direct light and the light from a plurality of light sources.